The present invention relates generally to the M60 machinegun and in particular to the unique parts of the M60 semi-automatic rifle used to convert the M60 machinegun or to produce a near clone of the M60 machinegun that operates only in semi-automatic firing mode. Collectors of military arms are usually persons who have served in the military or who grew up during times of military conflict and are intrigued by military arms. They prefer to have arms they can function and fire for events sponsored by legitimate fraternal organizations. These look-alikes are sometimes fired at the local gun ranges. Similar conversions have been made for other machineguns, but none with the unique sear block that travels with the existing bolt and can be removed with the bolt as a unit for service. The present invention has other features uniquely different from the M60 machinegun such as a receiver that cannot be converted to a machinegun, a bolt hold open stop, adjustable trigger, striker firing system, firing pin bushed for high pressures and Bureau of Alcohol Tobacco and Firearms approval for sale through class 1 licensed dealers.